Phase diagram and single-particle spectrum of CuO$_2$ layers within a variational cluster approach to the 3-band Hubbard model

TL;DR

This study uses a variational cluster approach to analyze the phase diagram and single-particle spectrum of the three-band Hubbard model in underdoped CuO$_2$ layers, revealing similarities to single-band models and detailed doping effects.

Contribution

It provides a detailed numerical analysis of the three-band Hubbard model, highlighting phase transitions and spectral features in underdoped cuprates with novel insights into electron and hole doping behaviors.

Findings

Identification of a mixed antiferromagnetic+superconducting phase at low doping.

Observation of a Zhang-Rice singlet band with coherent and incoherent parts.

Electrons preferentially occupy the upper Hubbard band, affecting phase stability.

Abstract

We carry out a detailed numerical study of the three-band Hubbard model in the underdoped region both in the hole- as well as in the electron-doped case by means of the variational cluster approach. Both the phase diagram and the low-energy single-particle spectrum are very similar to recent results for the single-band Hubbard model with next-nearest-neighbor hoppings. In particular, we obtain a mixed antiferromagnetic+superconducting phase at low doping with a first-order transition to a pure superconducting phase accompanied by phase separation. In the single-particle spectrum a clear Zhang-Rice singlet band with an incoherent and a coherent part can be seen, in which holes enter upon doping around $(\pi/2,\pi/2)$. The latter is very similar to the coherent quasi-particle band crossing the Fermi surface in the single-band model. Doped electrons go instead into the upper Hubbard band, first filling the regions of the Brillouin zone around $(\pi,0)$. This fact can be related to the enhanced robustness of the antiferromagnetic phase as a function of electron doping compared to hole doping.